Power Cables to stir pots with

[novisnick]

Dec 14, 2018 16:18:27 GMT -5 simpleman68 said:

Dec 14, 2018 13:18:05 GMT -5 DYohn said:

I have some 0000 AWG cable that is more than stiff enough to stir a pot with.

"That's what he said"

Somebody had to.....

Scott

Personally, I was going to post,,,

That’s what she said! 😋

[ttocs]

Dec 14, 2018 16:06:37 GMT -5 DYohn said:

The amplifier will draw what it draws. An under-sized power cable will heat up more than one designed with sufficient ampacity. If the power cable introduces enough resistance it will lower the line voltage, causing the amp to demand even more current, and around and round we go. The amp does not care it will just demand the current it needs, and the power cable will deliver that current right up to the point where it burns up. The only thing electrically that a larger power cable will do is deliver the demand current with fewer line losses and less heat due to losses.

Interesting, and I get all this. But the power cable wasn't heating up, the amp was. Is this because the amp wanted more Current than the cable could supply so the amp heated up, but since it wasn't on a continuous basis the cable didn't heat up like it would if it was connected to a hungry space heater??

[DYohn]

Dec 14, 2018 17:16:34 GMT -5 ttocs said:

Dec 14, 2018 16:06:37 GMT -5 DYohn said:

The amplifier will draw what it draws. An under-sized power cable will heat up more than one designed with sufficient ampacity. If the power cable introduces enough resistance it will lower the line voltage, causing the amp to demand even more current, and around and round we go. The amp does not care it will just demand the current it needs, and the power cable will deliver that current right up to the point where it burns up. The only thing electrically that a larger power cable will do is deliver the demand current with fewer line losses and less heat due to losses.

Interesting, and I get all this. But the power cable wasn't heating up, the amp was. Is this because the amp wanted more Current than the cable could supply so the amp heated up, but since it wasn't on a continuous basis the cable didn't heat up like it would if it was connected to a hungry space heater??

No, it's more likely that the voltage was being suppressed. A cable will supply infinite current right up until it melts.

[simpleman68]

Dec 14, 2018 16:44:42 GMT -5 novisnick said:

Dec 14, 2018 16:18:27 GMT -5 simpleman68 said:

"That's what he said"

Somebody had to.....

Scott

Personally, I was going to post,,,

That’s what she said! 😋

What kind of "she" is braggin' on their wood?

Scott

[KeithL]

If we're talking a two or three conductor cable, or more or less normal configuration, then you can forget about inductance.
In a normal power cbal,e, where you have two or three insulated wires, laying more or less parallel to each other, neither the inductance nor the capacitance is important.
(They may both vary significantly, but at the 60 Hz line frequency neither will be high enough to matter, and so both can be ignored.)

If the line cord had a resistance of one ohm, for every amp passing therough it, that line cord will drop (eat up) 1V.
So, if your line was delivering 120 VAC, and your amplifier used 10 Amps, the amplifier would see 110 VAC at its power input.
The power being consumed by that power cord works out to 10 watts (spread out over a six foot cord that might make it a bit warm).
Depending on the details of the circuitry inside the amplifier it MIGHT also run hotter.
(Some amplifiers simply run less efficiently when running from a lower line voltage.)
The amplifier might also have its maximum output power capability reduced a little bit.
(This will also depend on the details of that amplifier's design.)

In addition to this, some few amplifiers might have stability issues, because the line isn't providing the low impedance voltage source they expect it to.
This could cause some amplifiers to do odd things (but not most.)

It's also worth noting that the resistance of twelve feet of 18 gauge copper cable is actually still quite low.
(By the book, 18 gauge copper is 6.4 Ohms per 1000 feet...  so a six foot line cord, which is six feet each way, would have about 0.05 Ohms of resistance.)
So, in fact, an 18 gauge line cord should work just fine for an amplifier that draws 10 amps or so.
However, in practice, thin cords also tend to have thinner contacts, and less robust crimps and connections, which also add significantly to their resistance.)

Dec 14, 2018 14:13:54 GMT -5 ttocs said:

Also, I agree with Keith that there are inexpensive power cables out there. At this point I gotta say that the IEC connector I got is really, really nice in how well it grips the spades on the amp.

The two measurements I think are key in this case are Resistance and Inductance, both of which are lower than the 18 gauge cable.

So I'm left with the main question and some follow-ups: Why is the amp's operating temperature much lower? 

Is this because the resistance is lower? the inductances is lower? or both? Or does the grippier IEC connector contributing as well?

My initial answer without any facts to back it up is: Yes

[novisnick]

Dec 14, 2018 19:56:27 GMT -5 simpleman68 said:

Dec 14, 2018 16:44:42 GMT -5 novisnick said:

Personally, I was going to post,,,

That’s what she said! 😋

What kind of "she" is braggin' on their wood?

Scott

Ha! I thought you were happily married Scott! 😏😋

[ttocs]

Dec 14, 2018 20:06:19 GMT -5 KeithL said:

If the line cord had a resistance of one ohm, for every amp passing therough it, that line cord will drop (eat up) 1V.
So, if your line was delivering 120 VAC, and your amplifier used 10 Amps, the amplifier would see 110 VAC at its power input.
The power being consumed by that power cord works out to 10 watts (spread out over a six foot cord that might make it a bit warm).
Depending on the details of the circuitry inside the amplifier it MIGHT also run hotter.
(Some amplifiers simply run less efficiently when running from a lower line voltage.)
The amplifier might also have its maximum output power capability reduced a little bit.
(This will also depend on the details of that amplifier's design.)

In addition to this, some few amplifiers might have stability issues, because the line isn't providing the low impedance voltage source they expect it to.
This could cause some amplifiers to do odd things (but not most.)

It's also worth noting that the resistance of twelve feet of 18 gauge copper cable is actually still quite low.
(By the book, 18 gauge copper is 6.4 Ohms per 1000 feet...  so a six foot line cord, which is six feet each way, would have about 0.05 Ohms of resistance.)
So, in fact, an 18 gauge line cord should work just fine for an amplifier that draws 10 amps or so.
However, in practice, thin cords also tend to have thinner contacts, and less robust crimps and connections, which also add significantly to their resistance.)

Thanks for the great info Keith! I love explanations from engineers.

Regarding resistance, I measured both cord assemblies from plug spade to IEC contacts. The 6' long 18AWG cord measures 0.7 Ohms per leg so x2 = 1.4 Ohms. The 3' long DIY measures 0.1 Ohms per leg, x2 = 0.2 Ohms. And yes, I "zeroed" the probes on the Fluke 87 meter. I may be daft, but I'm not a ditz - assuming I know the difference.

Regarding amplifier operating temperature, the amp has been playing for several hours at a 97dB level which is well beyond what I would normally do for that period of time. I wanted to stress the system more than normal to prove the point to myself. I've been using a slow computer fan on top of the amp case for several years because of how hot it gets. Parts on the boards inside routinely get to over 150 degrees F at this volume without a fan. With the fan, nothing inside measures warmer than mid 120's. Now, without a fan, I can lay my hand on top of the case without getting burned. The case top temp is just over 130 degrees, and the internal parts that get hot are in the mid 140's. This is an improvement. BTW, the difference in temperature from really loud down to normal listening volume is not a huge amount, around 5-8 degrees, but it makes a big difference in how hot the top of the amp's case gets.

I also plugged the 18AWG cord into a Kill-A-Watt to see what the amp's Amps needs would be. Just being On, it draws 1.7A. Playing music it's hanging around 2A, with loud music getting to over 3A. I didn't previously know that the average Current draw would be this low. I thought for sure it would've been more like 5A typical, or does this change with speaker efficiency?

Questions:
1. Does an undersized power wire restrict the transient Current needs somehow?

2. Is it possible there is something wrong with this 18AWG power cord?

3. Is the better clamping force of the new IEC connector the big difference and wire gauge doesn't matter as much?

[ttocs]

I’m done making a power cable for the amp. After some experimental learning making a few cables I’ve landed on this:


SJOOW 12-3 cord by the foot at Home Depot.

PS5266SSANCCV4 Home Depot angle plug, this one is a 15A version of what I got before but the wire lugs are the same size as the 20A version and the spades are the same type.

HiFiKing CC-18(Cu) Red Copper Series IEC Plug Connector 15A/125V from Amazon.

This one is less than 0.1 Ohms per leg, my meter doesn’t resolve less than 0.1 Ohms. The cable is way better than what I was using and it's the length I want it to be. The amp has been operating with this new cable now for about 1-1/2 hours without a fan and playing the same music at the same volume as all my other tests and the amp is running even cooler than before! Nothing in the amp is over 141 degrees. (BTW I simply aim the temp gun through the air slots on the top of the amp.) I don't get it, but I am happy about it.

I’ll be making more power cables for other component to reduce the amount of wire behind the rack. I don’t expect a performance difference, it’s purely for neatness.

edit: Earlier today I tested the Current draw of the amp. My meter can record at 1ms intervals. I don't know what the proper time interval should be while checking the Current while playing music, but I did learn the following: At a 97dB SPL (-14 volume level on the XMC-1) at my listening position the amp would hit 7 Amps frequently, and it topped out at almost 7.5 Amps. I would venture a guess that my meter, which has a 10A limit on Current testing, might be getting in the way of an accurate test, but at least I know more now than I did before.